Multi-beam image forming apparatus and electrostatic latent image formation method

Abstract

An image forming apparatus includes a pattern formation control unit for forming a plurality of evaluation patterns by repeatedly turning on and off a plurality of light emitters arranged in a row in units of n dots (n is an integer equal to or greater than 1) to irradiate light to a photoconductor while changing write timings of the respective light emitters in a predetermined range, an adjustment unit for improving reliability of density difference information among the plurality of evaluation patterns, and a determination unit for obtaining information on densities of the respective evaluation patterns based on a detection result on the densities of the respective evaluation patterns and determining write timings derived from the evaluation pattern having the lowest or highest density as the write timings of the plurality of light emitters.

1 . An image forming apparatus, comprising:
 an image forming unit including a photoconductor and a light source with a plurality of light emitters arranged in a row at a predetermined interval and at a predetermined angle with respect to a main scanning direction of the photoconductor and adapted to form an electrostatic latent image on the photoconductor by emitting light corresponding to image data from the light source and form a toner image by developing the electrostatic latent image formed on the photoconductor with toner;   a detection unit for detecting a density of the toner image;   a pattern formation control unit for forming a plurality of evaluation patterns by repeatedly turning on and off the light emitters in units of n dots (n is an integer equal to or greater than 1) to irradiate light to the photoconductor while changing write timings of the respective light emitters in a predetermined range;   an adjustment unit for improving reliability of density difference information among the plurality of evaluation patterns; and   a determination unit for obtaining information on densities of the respective evaluation patterns based on a detection result on the densities of the respective evaluation patterns by the detection unit and determining write timings derived from the evaluation pattern having the lowest or highest density as the write timings of the plurality of light emitters.   
     
     
         2 . An image forming apparatus according to  claim 1 , wherein:
 the pattern formation control unit further forms predetermined fixed comparison patterns near the respective evaluation patterns;   the adjustment unit is a density corrector for causing the detection unit to detect densities of the respective evaluation patterns and the respective comparison patterns and calculating values obtained by subtracting the densities of the comparison patterns formed near the evaluation patterns from the densities of the evaluation patterns as corrected densities of the evaluation patterns; and   the determination unit determines the write timings adopted when the evaluation pattern having the lowest or highest density out of the calculated corrected densities was formed as the write timings of the plurality of light emitters.   
     
     
         3 . An image forming apparatus according to  claim 2 , wherein:
 the pattern formation control unit forms a plurality of comparison patterns near each evaluation pattern; and   the density corrector sets a value obtained by subtracting an average value of the densities of the plurality of comparison patterns formed near the evaluation pattern from the density of the evaluation pattern as the corrected density of the evaluation pattern.   
     
     
         4 . An image forming apparatus according to  claim 1 , wherein:
 the adjustment unit causes the evaluation patterns to be formed with an exposure light quantity larger than that of the light emitters when a normal image is formed; and   the determination unit causes the detection unit to detect the densities of the respective evaluation patterns and determines the write timings adopted when the evaluation pattern having the lowest or highest density out of the detected densities was formed as the write timings of the plurality of light emitters.   
     
     
         5 . An image forming apparatus according to  claim 1 , wherein:
 the pattern formation control unit includes a function of the adjustment unit and controls the image forming unit to form an evaluation chart by arranging the plurality of evaluation patterns in a sub scanning direction and form a plurality of evaluation charts having different shift cycles in the main scanning direction when the shift cycle is a period from one matching timing of formed dot rows to the next matching timing by successively shifting the write timings of the respective light emitters by a predetermined time; and   the determination unit calculates an ideal curve using positions where the density is lowest or highest in the respective evaluation charts and determines the write timings of the plurality of light emitters based on the ideal curve.   
     
     
         6 . An image forming apparatus according to  claim 1 , wherein:
 the pattern formation control unit includes a function of the adjustment unit and controls the image forming unit to form an evaluation chart by arranging the plurality of evaluation patterns in a sub scanning direction and form a plurality of evaluation charts having different shift cycles in the main scanning direction when the shift cycle is a period from one matching timing of formed dot rows to the next matching timing by successively shifting the write timings of the respective light emitters by a predetermined time; and   the determination unit detects the evaluation pattern having the lowest or highest density for each evaluation chart, extracts most detected evaluation pattern out of the detected evaluation patterns, and determines the write timings adopted when the extracted evaluation pattern was formed as the write timings of the plurality of light emitters.   
     
     
         7 . An electrostatic latent image formation method for forming an electrostatic latent image on a photoconductor by emitting light corresponding to image data from a light source, using the photoconductor and the light source with a plurality of light emitters arranged in a row at a predetermined interval and at a predetermined angle with respect to a main scanning direction of the photoconductor, comprising:
 forming a plurality of evaluation patterns by repeatedly turning on and off the light emitters in units of n dots (n is an integer equal to or greater than 1) to irradiate light to the photoconductor while changing write timings of the respective light emitters in a predetermined range;   performing an adjustment process of improving reliability of density difference information among the plurality of evaluation patterns;   detecting densities of the respective evaluation patterns;   obtaining information on the densities of the respective evaluation patterns based on a detection result on the densities; and   determining write timings derived from the evaluation pattern having the lowest or highest density as the write timings of the plurality of light emitters.   
     
     
         8 . An electrostatic latent image formation method according to  claim 7 , wherein:
 forming predetermined fixed comparison patterns respectively near the respective evaluation patterns;   detecting densities of the respective comparison patterns in detecting the densities of the respective evaluation patterns; and   calculating, as the adjustment process, values obtained by subtracting the densities of the comparison patterns formed near the evaluation patterns from the densities of the evaluation patterns as corrected densities of the evaluation patterns; and   determining the write timings adopted when the evaluation pattern having the lowest or highest density out of the calculated corrected densities was formed as the write timings of the plurality of light emitters.   
     
     
         9 . An electrostatic latent image formation method according to  claim 7 , wherein, as the adjustment process,
 forming the evaluation patterns with an exposure light quantity larger than that of the light emitters when a normal image is formed; and   determining the write timings adopted when the evaluation pattern having the lowest or highest density out of the detection result on the densities of the respective evaluation patterns was formed as the write timings of the plurality of light emitters.   
     
     
         10 . An electrostatic latent image formation method according to  claim 7 , wherein, as the adjustment process,
 forming a first evaluation chart by arranging the plurality of evaluation patterns in a sub scanning direction;   arranging a plurality of evaluation charts having shift cycles different from the first evaluation chart and another evaluation chart in the main scanning direction when the shift cycle is a period from one matching timing of formed dot rows to the next matching timing by successively shifting the write timings of the respective light emitters by a predetermined time;   calculating an ideal curve by using positions where the density is lowest or highest in the respective evaluation charts; and   determining the write timings of the plurality of light emitters based on the ideal curve.